1. Field of the Invention
This invention relates to a throttle for a two-stage carburetor and more particularly it relates to a mechanism for opening and closing secondary throttle valves of a multi-stage carburetor.
2. Description of the Prior Art
Multi-stage carburetors have primary and secondary induction passages with each primary and secondary passage opened and closed by a throttle valve. The primary and secondary throttle valves are operably linked together such that the secondary throttle valve is opened by the opening of the primary throttle valve only after the primary throttle valve has been substantially open. This operation may be accomplished by a delayed camming system. One such delayed camming system is disclosed in U.S. Pat. No. 3,259,376 issued to Baer on July 5, 1966.
Many of the throttle linkage systems disclosed in the prior art not only open the secondary throttle valve but also mechanically close the secondary throttle valve. One such linkage is disclosed in U.S. Pat. No. 3,328,008 issued to Gordon on June 27, 1967. The Gordon patent discloses a linkage which has a cam which abuts a lug on a secondary throttle lever valve which slightly opens the secondary throttle plate. A rod attaching the primary throttle to the secondary throttle further opens the secondary throttle upon further opening of the primary throttle. Upon closure of the primary throttle, the cam abuts an extension on the secondary throttle to close the secondary throttle.
U.S. Pat. No. 3,796,413 issued to Woods on March 12, 1974 and U.S. Pat. No. 3,328,007 issued to Bickhaus et al on June 27, 1967 disclose a mechanical linkage including a rod connected to the primary and secondary throttle with a slot in the secondary throttle lever to provide lost motion of the rod as it follows a primary throttle when it opens or closes. In such mechanical linkages, the primary throttle is free to move to a partially opened position before the secondary throttle is forced open.
U.S. Pat. No. 3,764,119 issued to Niebrzydoski on Oct. 9, 1973 and U.S. Pat. No. 3,575,385 issued to Szwargulski et al on Apr. 20, 1971 disclose a secondary throttle which is spring biased to the closed position. The secondary throttle has a backup closure mechanism generally comprising a complementary ear and tab coaxially mounted about the primary throttle pivot axis which are operably connected to a lever connected to the secondary throttle. The tab engages the ear which causes the lever to move the secondary throttle to the closed position after the primary throttle is substantially closed.